OVULES OF CYCADS 



325 



siderable size, but contain only a single large megaspore {p.) 

 within the several-laj'ered parenchymatous wall or niicdlus (».). 

 The delicate texture of the latter can be related to the presence 

 of a thick fleshy protective covering (0. and i.). This integument 



Fig. 1 85. — A, Megasporophyll of Cycas revoliUa with four ovules (about 

 half natural size). B, Mature megasporophyll of Encephalartos hil- 

 denbrandtii, bearing two seeds (about half natural size). D, Diagram 

 of longitudinal section of ovule of Boivenia speciabilis, and C, front end 

 of same enlarged. ar., archegonia ; «., inner fleshy layer of integu- 

 ment ; i.b., vascular bundle of inner series ; mi., micropyle ; «., 

 nucellus ; 0., outer fleshy layer of integument ; o.b., bundle of outer 

 series; ;^., female prothallus within megaspore; p.c, pollen chamber; 

 p.t., pollen tube ; s., stony laj'er of integument. (A and B original ; 

 C and D after Kershaw.) 



complete^ envelops the nucellus, and is indeed fused with it 

 except at its extreme apex. In this region the integument is 

 pierced b}? a narrow canal, the micropyle (»n'. ), leading down to the 

 tip of the nucellus, in which a conical cavity, the pollen chamber 

 {p.c), is formed b}' the breaking down of the tissue. The ovule is 



